Positive influence of hydrogen on the hot workability and dynamic recrystallization of a γ-TiAl based alloy

High temperature deformation behaviors of the unhydrogenated and hydrogenated Ti-46Al-2V-1Cr-0.3Ni (at%) alloys were investigated in the temperature range 1050-1200°C and strain rate range 0.001-1s^-1. The flow stress of the hydrogenated alloy was lower than that of the unhydrogenated alloy, which was mainly attributed to hydrogen-promoted lamellar decomposition, twinning and dynamic recrystallization. Processing maps of the unhydrogenated and hydrogenated alloys were constructed. The stability domain of the hydrogenated alloy was enlarged in comparison with that of the unhydrogenated alloy, meaning hydrogen enhanced the hot workability of the Ti-46Al-2V-1Cr-0.3Ni alloy. Hydrogen activated slip systems so that lamellar bending more easily occurred in the hydrogenated alloy, which made inter-lamellar fracture convert into trans-lamellar fracture. Therefore, crack propagation was restrained in the hydrogenated alloy during hot deformation. The critical strain of the hydrogenated alloy was less than those of the unhydrogenated alloy, meaning the dynamic recrystallization occurred earlier in the hydrogenated alloy. γ-phase discontinuous dynamic recrystallization was promoted due to hydrogen addition, leading to a consumption of plentiful dislocations, which restrained continuous dynamic recrystallization to some extent. Hydrogen-promoted discontinuous dynamic recrystallization was mainly attributed to hydrogen-promoted lamellar decomposition, twinning, and hydrogen-decreased stacking fault energy.